The present invention generally relates to a semiconductor device, and more specifically to a semiconductor device, a method for manufacturing this semiconductor device, and an electronic appliance with employment of this semiconductor device comprised of a film circuit on which a plurality of wiring films are formed while using an insulating layer as a base, one end of the wiring films are used as semiconductor element-sided terminals to be connected to electrodes of a semiconductor element, and an external terminal is formed on the other end of the wiring film; a semiconductor element, the respective electrodes of which are connected to the semiconductor element-sided terminals of the wiring films; a reinforcement plate adhered to the film circuit, for surrounding the semiconductor element; and a heat sink adhered to the reinforcement plate; in which the reinforcement plate, the film circuit, and the semiconductor element are sealed with each other.
As a semiconductor device, there is such a semiconductor device that the respective electrodes of a semiconductor element are bonded to tip portions of the respective leads (wiring films) of a film circuit, a space between this semiconductor element and the film circuit is sealed by using resin, and a ring-shaped reinforcement plate for surrounding the semiconductor element is adhered to a rear surface of the film circuit.
FIG. 1A and FIG. 1B are sectional views for indicating these conventional semiconductor devices. First, a description will now be made of the conventional semiconductor device shown in FIG. 1A. In this drawing, symbol "a" indicates a film circuit, symbol "b" shows a polyimide tape which may constitute a base of this film circuit, symbol "c" represents a wiring film which constitutes a lead, and symbol "d" shows an insulating layer for selectively covering a surface of the film circuit "a", which is located opposite to the base. This insulating layer is made of, for example, solder resist. Also, symbol "e" is a soldering ball formed in an opening "f" of the insulating layer "d", and this opening "f" exposes the surface of the lead "c". Also, this soldering ball constitutes an external terminal of the semiconductor device.
Symbol "g" indicates a semiconductor element, and an electrode of this semiconductor element "g" is bonded to a tip portion of such a portion projected into a device hall "h" of the lead "c". Symbol "i" indicates resin used to seal a space between the semiconductor element "g" and the film circuit "a". Symbol "j" represents a rectangular ring-shaped reinforcement plate. This reinforcement plate "j" is adhered via adhesive agent "k" to a position for surrounding the semiconductor element "g" of the rear surface of the film circuit "a".
Next, the conventional semiconductor device shown in FIG. 1B will now be explained. Symbol "a'" shows a film circuit constructed by a wiring film "c" which constitutes a lead that is formed on a rear surface of a polyimide tape "b" which constitutes a base of this film circuit. An opening "f" exposes the lead "c" formed in this polyimide tape "b", and a soldering ball "e" which constitutes an external terminal is formed in this opening "f". Similar to the semiconductor device shown in FIG. 5A, the semiconductor element "g" is connected to the lead "c" of the film circuit "a'", and a space between the semiconductor element "g" and the film circuit "a'" is sealed by using resin "i". Then, a rectangular ring-shaped reinforcement plate "j" is adhered via adhesive agent "k" to the rear surface of the film circuit "a'".
A description will now be made of an assembling method. First, the semiconductor element "g" is assembled on the film circuit a (a'). Next, the space between the film circuit a (a') and the semiconductor element "g" is sealed by using the resin "i". Thereafter, the reinforcement plate "j" is adhered to the rear surface of the film a (a'). Subsequently, the soldering ball "e" which constitutes the external terminal is formed.
On the other hand, according to the related art shown in FIG. 1A and FIG. 1B, no electric connection is made between the film circuit a (a') and the reinforcement plate "j". As a result, it is practically difficult to prevent the external noise from being entered. Also, a problem exists in that this conventional semiconductor device may not effectively prevent the external noise producing source.
Also, conventionally, after the semiconductor element "g" has been assembled to the film circuit a (a'), the space between the semiconductor element and the film circuit is sealed by using the resin. Thereafter, the reinforcement plate "j" is adhered to the film circuit a (a'). As a result, there is another problem that since the adhesive agent "i" is largely extruded, the reinforcement plate "j" can be hardly mounted. As a consequence, as indicated in FIG. 1B, such a plate having a large hole "l" must be employed as the reinforcement plate "j". However, this may cause the reinforcement effect to be deteriorated, resulting in an unfavorable effect. In other words, the reinforcement effect of the semiconductor device shown in FIG. 1B should be deteriorated.
To solve such a problem, the applicant has developed the following techniques as proposed Japanese Patent Application No. 8-54478 (which is laid-open in Japanese Unexamined Patent Application No. 9-246315). That is, the noise withstanding characteristics of the semiconductor device can be increased, and further the reinforcement plate can be mounted on the film circuit without problems. This proposed semiconductor device is featured by that the wiring film which constitutes the ground line formed on the peripheral portion thereof is provided on the film circuit, and the reinforcement plate owns the conductivity characteristics. Then, the wiring film which constitutes this ground line is electrically connected to this conductive reinforcement plate at the above-described peripheral portion of the film circuit. As a consequence, the reinforcement plate for surrounding the semiconductor element may be used as the ground line, namely may electrostatically shield other elements.
This semiconductor device may be manufactured as follows: The reinforcement plate is adhered to the film circuit. Thereafter, the semiconductor element is located at the position surrounded by the reinforcement plate, and the respective electrodes of this semiconductor element are bonded on the semiconductor element-sided terminal of the film circuit. Subsequently, the reinforcement plate, the film circuit, and the semiconductor element are sealed with each other. In other words, in accordance with such a semiconductor device manufacturing method, after the reinforcement plate has been adhered to the film circuit, the semiconductor element is assembled to the film circuit, and then is sealed. As a consequence, there is completely no risk that the sealing agent for sealing the space between the semiconductor element and the film circuit blocks adhesion of the reinforcement plate to the film circuit. As a consequence, the reinforcement plate can be mounted without any problem. Also, there is no need to employ such a reinforcement plate having the large hole as in the semiconductor device shown in FIG. 1B, taking account of the assembling condition. Accordingly, there is no risk that the reinforcement effect is deteriorated.
FIG. 2A and FIG. 2B represent the above-described semiconductor device. This semiconductor device will now be simply explained. The wiring films 3E and 3e which constitute the ground line extended on the peripheral portion of the film circuit 1, and while using the conductive reinforcement plate 25, the wiring film which constitutes this ground line 3E is electrically connected to this conductive reinforcement plate 25 at the peripheral portion of the film circuit 1 by using, for example, conductive paste 26. The heat sink 27 is adhered to the rear surface of the film circuit 1 and the semiconductor element 4, if necessary.
Then, this semiconductor device is manufactured as follows. The reinforcement plate 25 is adhered to the film circuit 1. Thereafter, the semiconductor element 4 is located at the position surrounded by the reinforcement plate 25, and the respective electrodes of this semiconductor element 4 are bonded with the semiconductor element-sided terminals of the film circuit 1. Subsequently, the reinforcement plate 25, the film circuit 1, and the semiconductor element 4 are sealed with each other by using sealing agent 24. It should be understood that in the drawings, reference numeral 2 indicates an insulating film, reference numeral 3 denotes a wiring film (lead), reference numeral 6 shows an electrode of the semiconductor element 4, reference numeral 7 is elastic adhesive agent for adhering the conductive reinforcement plate 25 to the film circuit 1, reference numeral 16 indicates a bump of the wiring film (lead), and reference numeral 28 shows a dam for blocking a flow of the sealing resin 24 to the peripheral portion.
On the other hand, in accordance with the above-explained related art shown in FIG. 2A and FIG. 2B, the reinforcement plate can be surely used as the electrostatic shielding means, which may achieve the superior feature. However, there is a limit to suppress the noise generation. This is because the following limitation exists in increasing of the stray capacitance straying between the power supply line and the ground line (between power supply terminals, for example, between V.sub.DD and V.sub.SS, or between V.sub.CC and V.sub.EE). As a consequence, it is difficult to absorb the generated noise by the stray capacitance. This reason will now be described more in detail.
The level at the power supply terminal, and the ground level are varied due to the load variation and the like, which may directly cause the noise. Although this noise may be absorbed by the stray capacitance existing between the power supply and the ground, if this stray capacitance is small, then the noise cannot be sufficiently absorbed. As a consequence, the larger the stray capacitance between the power supply and the ground is increased, the better the noise absorption becomes. However, in accordance with the conventional semiconductor device shown in FIG. 2 FIG. 2A and FIG. 2B, this stray capacitance is constructed only of the stray capacitance between the power supply wiring film and the ground wiring film, and also of the stray capacitance between the reinforcement plate connected to the ground (or power supply) and the power supply wiring film (or ground wiring film).